The battery has become a primary power source for many portable electronic devices such as radios, hearing aids, watches, calculators, and the like. In order to maintain the overall electronic devices as compact as possible, the electronic devices are usually designed with cavities to accommodate miniature batteries as their source of power. The cavities are usually made so that a battery can be snugly positioned therein thus making electronic contact with appropriate terminals within the device. A major potential problem in the use of battery powered devices of this nature is that if the battery bulges, it usually becomes wedged within the cavity of the device which sometimes can result in damage to the device. One cause of cell bulging or other distortion of the cell's overall physical dimensions is due to the expansion of the cathode during discharge or during abusive discharge conditions. For example, in nonaqueous lithium/solid cathode systems, the cathode may expand and move into the anode compartment of the cell during discharge. Especially with improperly balanced cell components or under abusive cell conditions, it is common for this cathode expansion to cause cell distortion (bulging) which, in turn, may cause damage to the electronic device in which the cell is used. Since this type of cell distortion is due to the physical expansion of the cathode, then a possible solution to minimize any overall cell distortion is to provide a void or cavity within the cell to accommodate the expansion of the cathode. Within electronic technology geared to miniaturization, it becomes necessary to package the power supply in a miniature type package so that the device it is to power can be reduced in size. Consequently, providing cavities within the cell system to accommodate any electrode expansion is not economically feasible.
Another disadvantage of excessive cathode expansion is that the increase in force of the cathode against the anode via the separator could alter the resistive characteristics of the cell resulting in undesirably low energy output during certain cell applications. For example, it has been observed that in a FeS.sub.2 /lithium cell, excessive expansion of FeS.sub.2 occurs that causes the cell to bulge and also results in low service and/or premature reduction in the cell's pulsing capability during discharge. In a like manner, insufficient expansion of the cathode would not provide a continuous optimum contact between the cathode and anode which could also result in changing the resistive characteristics of the cell.
It is, therefore, an important object of this invention to provide a compact cell assembly which employs a mixture of solid active cathodic materials that will volumetrically expand during cell discharge to a degree substantially equal to the volumetric contraction of the anode during discharge thereby providing a substantially constant volume cell.
Another object of the present invention is to provide a cell that will not excessively bulge in a device during its useful discharge period.
Another object of the present invention is to provide a cell having a cathode comprising a physical mixture of CuO and FeS.sub.2 in conjunction with a lithium anode and a suitable electrolyte that overall remains substantially volumetrically constant during discharge.
Another object of the present invention is to provide a cell having a cathode comprising a physical mixture of Bi.sub.2 O.sub.3 and FeS.sub.2 in conjunction with a lithium anode and a suitable electrolyte that overall remains substantially volumetrically constant during discharge.
The foregoing and additional objects will become more fully apparent from the following description.